1. Pedigree
Analysis
©2005 Lee Bardwell

2. Autosomal vs. sex-linked traits
Autosomal traits are caused by genes on autosomes (chrms #1- #22)
e.g., we speak of autosomal recessive or autosomal dominant traits or diseases
Sex-linked traits are caused by genes on the sex chrms (X or Y)
e.g., we speak of X-linked recessive or X-linked dominant traits or diseases
©2004 Lee Bardwell

3. Dominant inheritance *Assuming 100% penetrance
If D is the disease allele and d is normal, then only dd genotypes are disease free*
Dominant trait/disease found in every generation*
Affected kid never** born to unaffected parents
*Assuming 100% penetrance
**Assuming no new mutation

4. Recessive inheritance
If d is the disease allele and D is normal, then only dd genotypes are affected
typically not seen in every generation
Affected kid can be born to unaffected parents

5. X-linked recessive inheritance
Rules for recessive inheritance apply
Mostly males are affected

6. X-linked dominant inheritance
Rules for dominant inheritance apply
Dad’s pass disease to all of their daughters and none of their sons

7. X-linked genes (and X-linked diseases)...
Males: haploid (= hemizygous) for most X-linked genes.
--> men are more frequently affected by diseases caused recessive alleles of X-linked genes
©2001 Lee Bardwell

8. Female carrier* mates with normal male
*of x-linked
recess. disease
Sperm
F x M
XNXA XNY XN Y F
XNXN M
XNY XN
normal
normal
Eggs F
XAXN
carrier M
XAY
affected XA
Half* her daughters will be carriers
Half* her sons will be affected
*on average
©2001 Lee Bardwell`

9. Affected male* mates with normal female
*with x-linked
recess. disease
Sperm
F x M
XNXN XAY XA Y F
XNXA
carrier M
XNY XN
normal
Eggs M
XNY
normal XN
All his daughters will be carriers
None of his sons will be affected
©2001 Lee Bardwell

10. Some X-linked recessive human diseases
Hemophilia A
Hemophilia B
Red-green color blindness
Duchenne muscular dystrophy
Retinitis pigmentosum (one of many loci)
Lesch-Nyhan Syndrome
Many others
No need
to memorize
©2000 Lee Bardwell

11. Affected male mates with normal female
X-linked dominant disease
Affected male mates with normal female
Sperm
F x M
XNXN XAY XA Y F
XNXA
affected M
XNY XN
normal
Eggs M
XNY
normal XN
All his daughters will be affected
None of his sons will be affected
©2001 Lee Bardwell

12. Affected female mates with normal male
X-linked dominant disease
Affected female mates with normal male
Sperm
F x M
XNXA XNY XN Y
Work this out
for yourself XN
Eggs XA
_______of her daughters will be _______
_______of her sons will be ____________
©2005 Lee Bardwell`

13. Some X-linked dominant human diseases
Incontinentia Pigmenti
Hypophosphatemic Rickets
Charcot-Marie-Tooth disease
Chondrodysplasia Punctata
No need
to memorize
©2005 Lee Bardwell

14. Pedigree Analysis I II Mating Normal Normal Female Male 1st born
Affected
Siblings
See H&J pp
©2001 Lee Bardwell

15. Fig. 2.17. Conventional symbols used in depicting human pedigrees.
Warning:

16. Pedigree showing X-linked recessive inheritanceII
III IV
©2002 Lee Bardwell

17. Could this be autosomal recessive?II
III IV
©2002 Lee Bardwell

18. Could this be X-linked dominant?II
III IV
©2002 Lee Bardwell

19. Could this be autosomal dominant?II
III IV
©2002 Lee Bardwell

20. *both autosomal and x-linked
If two affected parents have an unaffected kid, recessiveness* can be ruled out
(assuming 100% penetrance)
*both autosomal and x-linked
©2001 Lee Bardwell

21. *both autosomal and x-linked
If unaffected parents have an affected kid, dominance* can be ruled out
*both autosomal and x-linked
©2001 Lee Bardwell

22. If unaffected parents have an affected daughter, dominance and x-linked recessive can be ruled out
©2000 Lee Bardwell

23. If affected woman has unaffected son, or unaffected man has affected daughter, x-linked recessive can be ruled out
NOT XR
NOT XR
©2001 Lee Bardwell

24. If unaffected woman has affected son, or affected man has unaffected daughter, x-linked dominant can be ruled out XD XD
©2001 Lee Bardwell

25. Fig. 2.18. Inheritance of dominant gene for Huntington disease

26. Inheritance of dominant trait
Could this be autosomal recessive?
Inheritance of dominant trait

27. Genetic Counseling
A woman’s brother died from Tay Sach’s Disease (autosomal recessive, lethal), but she is unaffected. What are the chances that she is a carrier of the disease?
©2000,2005
Lee Bardwell
2/3 (67%) B. 1/2 (50%) C. 1/4 (25%)
D. 1/6 (17%) E. 1/8 (12.5%)

28. Hint
A woman’s brother died from Tay Sach’s Disease (autosomal recessive, lethal), but she is unaffected. What are the chances that she is a carrier of the disease?
©2000,2005
Lee Bardwell
2/3 (67%) B. 1/2 (50%) C. 1/4 (25%)
D. 1/6 (17%) E. 1/8 (12.5%)

29. The answer is… D d A B DD Dd D d Dd dd C D
2/3 (67%) B. 1/2 (50%) C. 1/4 (25%)
D. 1/6 (17%) E. 1/8 (12.5%)
©2005 Lee Bardwell

30. Problem 2
Assuming your grandfather is a carrier (heterozygote) for a rare recessive, disease causing allele of a given gene,
What’s the chance that you are also a carrier of this allele?
©2001 Lee Bardwell

31. IF THEN ? you 2/3 B. 1/2 C. 1/4 D. 1/6 E.1/8 D E F G H ©2001,2005
Lee Bardwell

32. = Chance that you got a given allele from Grandpa D
1/2 (50% chance) mom
got the allele F G
1/2 (50% chance) she gave
it to you if she had it H
1/2 x 1/2 = 1/4
= Chance that you got a given allele from Grandpa D
©2000 Lee Bardwell

33. Problem 3
Your grandfather’s sister had cystic fibrosis (rare, autosomal recessive). That’s the only case in your family.
(A) What’s the chance that you are a carrier of CF?
2/3 B. 1/2 C. 1/4
D. 1/6 E.1/8
©2001 Lee Bardwell

34. Your grandfather’s sister had CF but he, his parents, and his descendants are unaffected, as are those who married into the family A B
2/3
1/2
1/4
1/6
1/8 C D E F G H
you
©2001 Lee Bardwell

35. D d A B DD Dd D
2/3 d Dd dd C D E F G H
you
©2001 Lee Bardwell

36. IF D E F G
THEN ? H
you
©2001 Lee Bardwell

37. ANSWERS
A. 1/4 = Chance that you got any particular allele from from grandpa
B. 1/6 = correct answer = 1/4 (see A) x 2/3 (chances that grandpa was a carrier)
©2001 Lee Bardwell